The disclosure of Japanese Patent Application No. 2000-214108 filed on Jul. 14, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates in general to a fluid-filled vibration-damping device, which exhibits a vibration damping or isolating effect based on flows or resonance of a non-compressible fluid contained therein. More particularly, the present invention is concerned with a novel fluid-filled vibration damping device which has a plurality of orifice passages tuned to respective different frequency bands of input vibrations and exhibits an excellent vibration damping effect with respect to the input vibrations having different frequencies or over a wide frequency range, based on the flows of the non-compressible fluid through these orifice passages.
2. Discussion of the Related Art
As one type of a vibration damper interposed between two members of a vibration system so as to connect these two members in a vibration damping manner or mount one of these members on the other member in a vibration damping manner, there is known, as disclosed in JP-U-61-190051, for example, a fluid-filled vibration damping device which includes: a first and a second mounting member that are disposed in mutually spaced-apart relationship with each other; an elastic body elastically connecting the first and second mounting members and partially defining a pressure-receiving chamber filled with a non-compressible fluid; and an easily deformable flexible diaphragm partially defining an equilibrium chamber filled with the non-compressible fluid and held in fluid communication with the pressure-receiving chamber through a first orifice passage. Such a known fluid-filled vibration-damping device is capable of exhibiting an excellent vibration damping effect based on resonance of the fluid flowing through the first orifice passage, which effect would not be achieved by only the elasticity of the elastic body. Therefore, the fluid-filled vibration-damping device is preferably usable as an engine mount for an automotive vehicle, for example.
Generally, the vibration damping or isolating effect of the known fluid-filled vibration damping device based on the flows or resonance of the fluid is exhibited with respect to only the particular input vibrations over a limited frequency range to which the first orifice passage is tuned. In particular, when the frequency of the input vibration is higher than the frequency band to which the first orifice passage is tuned, a resistance to flow of the fluid through the first orifice passage tends to be increased, making it difficult for the device to exhibit a satisfactory damping effect based on the fluid flows through the first orifice passage. In this case, the fluid-filled vibration-damping device exhibits a high dynamic spring constant, resulting in significant deterioration of the vibration damping characteristics.
To cope with this drawback, there is proposed another structure of the fluid-filled vibration damping device wherein the pressure-receiving chamber is partially defined by an elastically displaceable elastic wall member, as disclosed in JP-A-2-129427, for example. In this structure, the elastic wall member is displaced at a suitable frequency so that a periodic pressure change generated in the pressure-receiving chamber upon application of the higher frequency vibrations is reduced or absorbed, for preventing or minimizing an excessive increase in the dynamic spring constant of the device. There is also proposed yet another structure, as disclosed in JP-A-7-71506, wherein a partition member is disposed within the pressure-receiving chamber so as to divide the pressure-receiving chamber into two sections, namely a primary fluid chamber partially defined by the elastic body and a auxiliary fluid chamber partially defined by the elastic wall member, and a second orifice passage is formed for fluid communication between the primary and auxiliary fluid chambers. In this structure, the vibration damping device exhibits a low dynamic spring constant and an accordingly high vibration isolating effect based on flows of the fluid through the second orifice passage, upon application of high-frequency vibrations.
However, even in the provision of the elastic wall member or the second orifice passage, as described above, the fluid-filled vibration damping device still suffers from significant increase in the dynamic spring constant when the frequency of the input vibration is higher than the frequency band to which the elastic wall member or the second orifice passage is tuned, resulting in significant deterioration of the vibration damping characteristics of the device with respect to the higher frequency vibrations. Thus, the known fluid-filled vibration damping device suffers from significant difficulty in exhibiting an excellent vibration damping or isolating effect with respect to the input vibrations over a sufficiently wide frequency range.
It is therefore an object of the present invention to provide a fluid-filled vibration damping device which is novel in construction and which is capable of exhibiting an excellent vibration damping or isolating effect based on flows or resonance of a non-compressible fluid contained therein, with respect to input vibrations over a sufficiently wide frequency range.
The above and other objects of this invention may be attained according to the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to those modes of the invention and combinations of the technical features, but may otherwise be recognized based on the thought of the present invention that disclosed in the whole specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) A fluid-filled vibration damping device comprising: a first and a second mounting member which are spaced apart from each other; an elastic body elastically connecting the first and second mounting members and partially defining a pressure-receiving chamber, the pressure-receiving chamber being filled with a non-compressible fluid whose pressure is changed upon application of a vibrational load between the first and second mounting members; an easily deformable flexible diaphragm partially defining an equilibrium chamber on one of opposite sides thereof, the equilibrium chamber being filled with the non-compressible fluid and has a volume easily variable; a first orifice passage for fluid communication between the pressure-receiving chamber and the equilibrium chamber; an elastic wall member being elastically displaceable and partially defining the pressure-receiving chamber; a restricting member disposed on one of opposite sides of the elastic wall member which is remote from the pressure-receiving chamber, the elastic wall member being elastically pressed to the restricting member; a working air chamber partially defined by the other side of the flexible diaphragm remote from the equilibrium chamber; and a negative pressure-regulating device adapted to apply different negative pressures to the working air chamber, depending upon frequencies of vibrations to be damped.
In the above-indicated mode (1) of the present invention, the pressure of the fluid within the pressure-receiving chamber is varied due to the elastic deformation of the elastic body, upon application of vibrational loads between the first and second mounting members. (a) Upon application of the vibrational loads over a low frequency band, the fluid is forced to flow through the first orifice passage between the pressure-receiving chamber and the equilibrium chamber, based on the fluid pressure difference between the pressure-receiving chamber and the equilibrium chamber, whereby the vibration damping device exhibits a high vibration damping effect with respect to the low frequency vibrations based on the resonance of the fluid flowing through the first orifice passage. (b) Upon application of the vibrational loads over a frequency band which is higher than the frequency band to which the first orifice passage is tuned, the fluid is forced to flow within the pressure-receiving chamber based on the elastic deformation of the elastic wall member, while the first orifice passage is substantially closed, whereby the vibration damping device exhibits a high vibrational isolating effect with respect to the relatively higher frequency vibrations, based on the resonance of the fluid flowing within the pressure-receiving chamber.
When the negative pressure is applied to the working air chamber, the flexible diaphragm is attracted to the side of the working air chamber, resulting in a reduced fluid pressure in the equilibrium chamber. The reduced pressure in the equilibrium chamber is transmitted to the pressure-receiving chamber through the first orifice passage, whereby the elastic wall member partially defining the pressure-receiving chamber is attracted to the side of the pressure-receiving chamber owing to its elastic deformation. Namely, the reduced fluid pressure applied to the elastic wall member acts to displace the elastic wall member in a direction remote from the restricting member against the elastic force of the elastic wall member in a direction toward the restricting member. This results in elastic deformation and displacement of the elastic wall member in the direction remote from the restricting member. In this condition, the elastic wall member is likely to be elastically deformable without being restricted by the restricting member. Thus, the spring constant of the elastic wall member is decreased, leading to a low wall spring stiffness of the pressure-receiving chamber. In this respect, the wall spring stiffness of the pressure-receiving chamber should be interpreted to mean an amount of fluid pressure change in the pressure-receiving chamber required to change a volume of the pressure-receiving chamber by a unit volume.
The application of the negative pressure to the working air chamber causes the decrease of the spring constant of the elastic wall member, so that the resonance frequency of the fluid flowing within the pressure-receiving chamber due to the elastic deformation of the elastic wall member shifts to the more lower frequency band. In the present fluid-filled vibration-damping device, therefore, the resonance frequencies of the fluid flowing within the pressure-receiving chamber can be changed by alternately turning ON and OFF the application of the negative pressure to the working air chamber, or alternatively by suitably regulating the level of the negative pressure applied to the working air chamber. Thus, the fluid-filled vibration-damping device can exhibit an excellent vibration damping or isolating effect with respect to vibrations over the different frequency bands.
In the fluid-filled vibration damping device constructed according to the present mode (1), the negative pressure applied to the working air chamber is not particularly limited, provided the negative pressure force is large enough to attract the elastic wall member to the side of the pressure-receiving chamber against the elastic force of the elastic wall member in the direction toward the restricting member, for thereby changing the wall spring stiffness of the pressure-receiving chamber. For instance, the working air chamber may be alternately exposed to the atmosphere and the negative pressure having a predetermined constant value.
Alternatively, the working air chamber is exposed to the negative pressure whose value is varied gradually or continuously. Further, the elastic wall member, partially defining the pressure-receiving chamber may be selected from a rubber plate member made of rubber material overall, or a canvas-reinforced or a rigid-material reinforced rubber plate member, for example. The elastic wall member may otherwise be formed of a combination of a rigid movable plate made of metal or synthetic resin materials and an elastic support fixed to the peripheral portion of the rigid movable plate for elastically support the rigid movable plate.
(2) A fluid-filled vibration damping device according to the above-indicated mode (1), wherein at least one of the elastic wall member and the restricting member has an abutting projection projecting therefrom toward the other of the elastic wall member and the restricting member, the elastic wall member being partially pressed to the restriction member at the abutting projection.
In this mode (2), the abutting part of the elastic wall member with respect to the restricting member is limited to the abutting projection. Therefore, the elastic wall member is likely to be elastically deformable at the part other than the abutting part, where the elastic wall member is not pressed to the restricting member, resulting in stability of the elastic deformation characteristics of the elastic wall member, and a resultant stability of the vibration damping characteristics of the damping device. Thus, the fluid-filled vibration-damping device of this mode (2) can exhibit a desired damping effect with high stability.
In this mode (2), at least one of the abutting parts of the elastic wall member and the restricting member is made of an elastic body, preferably. This arrangement is effective to reduce an impact noise upon collision of these abutting parts of the elastic wall member and the restricting member. It is also possible to provide a plurality of abutting projections between the elastic wall member and the restricting member. These abutting projections have different heights so that these abutting projections are sequentially brought into abutting contact with the elastic wall member or the restricting member, depending upon the level of the negative pressure applied to the working air chamber. This arrangement makes it possible to gradually change the elastic characteristics of the elastic wall member with high clarity and stability, depending upon the level of the negative pressure applied to the working air chamber. Preferably, each abutting projection is an annular member coaxially disposed about the center axis of the elastic wall member. The annular member extends continuously or discontinuously in its circumferential direction. The annular abutting projection ensures a stability of the elastic deformation of the elastic wall member with the each abutting projection held in abutting contact with the elastic wall member or the restricting member, leading to a resultant stability of the spring characteristics of elastic wall member.
(3) A fluid-filled vibration damping device according to the above-indicated mode (1) or (2), further comprising: a partition member which is adapted to divide the pressure-receiving chamber into a primary fluid chamber partially defined by the elastic body and an auxiliary fluid chamber partially defined by the elastic wall member; and a second orifice passage for fluid communication between the primary fluid chamber and the auxiliary fluid chamber, the second orifice passage being tuned to a frequency band which is higher than the frequency band to which the first orifice passage is tuned. In this mode (3) of the invention, the second orifice passage is formed within the pressure-receiving chamber for clearly defining the fluid passage through which the fluid flows within the pressure-receiving chamber upon application of the vibrational loads between the first and second mounting members. The presence of the second orifice passage facilitates flows of the fluid within the pressure-receiving chamber. The length and cross sectional area of the second orifice passage is suitably dimensioned so that the fluid-filled vibration damping device can exhibit an excellent vibration damping or isolating effect with respect to input vibrations over the specific frequency range.
(4) A fluid-filled vibration damping device according to the above-indicated modes (3), wherein one of the first and second mounting members is attached to a power unit of the vehicle, and the other of the first and second mounting members is attached to a body of the vehicle, such that the power unit is mounted on the body of the vehicle in a vibration damping fashion, the first orifice passage being tuned to a frequency band corresponding to that of engine shakes, the second orifice passage being tuned to a frequency band corresponding to a booming noise with the elastic wall member pressed to the restricting member, while being tuned to a frequency band corresponding to engine idling vibrations with the working air chamber exposed to the negative pressure.
In this mode (4), the vibration damping device is capable of exhibiting high damping effect with respect to vibrations required to damp in the vehicle, namely, the engine shakes and booming noises generated during running of the vehicle, and the engine idling vibrations generated during idling of the engine of the vehicle. While the negative pressure is applied to the working air chamber so that the vibration damping device exhibit a desired damping effect with respect to the engine idling vibrations, the negative pressure having a relatively high level is available from the air intake system of the engine, when the engine is in the engine idling mode. Thus, the vibration-damping device of this mode (4) effectively utilizes this high negative pressure to effectively control the damping effect thereof.
(5) A fluid-filled vibration damping device according to any one of the above-indicated modes (1)-(4), wherein the elastic wall member partially defines an interior space on the other side thereof remote from the pressure-receiving chamber, the interior space permitting an displacement of the elastic wall member and being exposed to the atmosphere through a communication hole.
In this mode (5) of the invention, the interior space partially defined by the elastic wall member is exposed to the atmosphere. This arrangement permits a stable displacement of the elastic wall member based on the negative pressure, which is applied to the working air chamber and acts on the elastic wall member via the non-compressible fluid filling the pressure-receiving chamber. Namely, the interior space exposed to the atmosphere is effective to prevent occurrence of a negative pressure within the interior space upon displacement of the elastic wall member, so that the elastic wall member is desirably displaced by applying the suitably regulated negative pressure to the working air chamber, without adverse influence of the occurrence of the negative pressure in the interior space. According to this mode (5) of the invention, the state or attitude of the elastic wall member may be desirably and effectively controlled by applying the suitably regulated negative pressure to the working air chamber. In addition, the interior space that is always exposed to the atmosphere is effective to reduce or prevent variation in temperature in the interior space, thereby eliminating or reducing possibility of undesirably variation in elastic characteristics of the elastic wall member and in the damping characteristics of the device, due to the temperature variation.
(6) A fluid-filled vibration damping device according to any one of the above-indicated modes (1)-(5), further comprising a pressure detecting device for detecting a pressure value of the non-compressible fluid, wherein the negative pressure applied to the working air chamber is corrected based on the pressure value detected by the pressure detecting device.
In this mode (6), the pressure of the fluid filled within he device is detected as a measurement. The obtained measurement is compared with the target value. Based on the difference between the obtained measurement and the target value, the negative pressure value applied to the working air chamber is controlled in a feedback fashion so that the negative pressure applied to the working air chamber has a target pressure value. This permits stabilized application of the negative pressure to the working air chamber and the elastic wall member, even if the negative pressure in the vacuum source varies. Thus, the vibration-damping device of the present mode (6) can exhibit desired vibration damping characteristics with high stability.
(7) A fluid-filled vibration damping device according to any one of the above-indicated modes (1)-(6), wherein the second mounting member includes a recess open to the first mounting member and a partition wall disposed within the recess such that the partition wall is located in an intermediate portion of the recess as seen in a depth direction of the recess, so as to fluid-tightly divide an interior space of the recess into a bottom-side space and an open-side pocket, the flexible diaphragm being disposed in the bottom-side space such that the flexible diaphragm fluid-tightly divide the bottom-side space into the equilibrium chamber and the working air chamber formed on the opposite sides of the flexible diaphragm, the elastic body elastically connecting the first mounting member and an open end portion of the open-side pocket of the second mounting member so that the open end portion of the open-side pocket is fluid-tightly closed by the elastic body, the elastic wall member being disposed in the bottom side of an interior space of the open-side pocket such that a peripheral portion of the elastic wall member is supported by an inner wall surface of the open-side pocket, while being pressed onto the partition wall, the pressure-receiving chamber being partially defined by and formed between the elastic body and the elastic wall member.
In this mode (7), the second mounting member has the above-indicated specific structure, namely has the recess. The recess of the second mounting member is effective to arrange the pressure-receiving chamber, equilibrium chamber, the working air chamber and the elastic wall member therein. This makes it possible to construct a desired fluid-filled vibration-damping device with a reduced number of component members and with a simple structure. While the space for installing an engine mount in a vehicle is limited, the present mode (7) permits to provide an engine mount with a compact size.